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Environmental fate & pathways

Phototransformation in air

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Description of key information

Calculation with AOPWIN v1.92 (EPIWIN software by US-EPA), overall gas-phase reaction constant: 16.04 E-12 cm³/molecules-sec (= 0.14 m³/molecules-day), with an half-life of 0.67 d (8.00 h) by assuming a 12 h day with an OH rate constant of 1.5E6 OH/cm³ and 25 °C. 

Key value for chemical safety assessment

Half-life in air:
8 h
Degradation rate constant with OH radicals:
0.14 m³ molecule-1 d-1

Additional information

The phototransformation in air was calculated with the computer program AOPWIN (v1.92a) program made available by the U.S. Environmental Protection Agency. This program estimates the rate constant for the atmospheric, gas-phase reaction between photochemically produced hydroxyl radicals and organic chemicals. It also estimates the rate constant for the gas-phase reaction between ozone and olefinic/acetylenic compounds. The rate constants estimated by the program are then used to calculate atmospheric half-lives for organic compounds based upon average atmospheric concentrations of hydroxyl radicals and ozone. The estimation methods used by AOPWIN are based upon the structure-activity relationship (SAR) methods. For tributyl citrate an overall OH rate constant (gas-phase reaction constant) of 16.04 E-12 cm3/molecules-sec and a half-life of 0.67 days (8.00 hours) was calculated, assuming a 12- hr day with an OH rate constant of 1.5 E6 OH/cm³. Reaction with N, S and –OH is estimated to be 0.14 E-12 cm3/molecules-sec, no ozone reaction is estimated for the compound. The assumed “Hydrogen Abstraction” gives a value of 15.90 E-12 cm³/molecule-sec, which is almost equal to the overall OH rate constant of the compound. All calculations were performed supposing a surrounding temperature of 25 °C. Thus it can be concluded that the substance will be rapidly degraded in air.